What are the physical properties of alkenes?

Alkenes are hydrocarbons that are colourless, odourless, less dense than water, and insoluble in water but soluble in organic solvents.

Alkenes are a type of hydrocarbon, which means they are composed of hydrogen and carbon atoms. They are unsaturated hydrocarbons, characterised by the presence of a carbon-carbon double bond. This double bond gives alkenes their unique properties and reactivity.

Physically, alkenes are typically colourless gases, liquids or low melting point solids, depending on the size of the molecule. They are odourless, unless substituted with an odorous group. Alkenes are less dense than water, which means they will float on the surface of water. This property is important in environmental incidents involving hydrocarbon spills, where alkenes can spread across the surface of bodies of water.

Alkenes are insoluble in water due to their non-polar nature. Water is a polar molecule, and 'like dissolves like', meaning polar substances dissolve in polar solvents and non-polar substances dissolve in non-polar solvents. However, alkenes are soluble in organic solvents, such as ether or chloroform, which are also non-polar.

The physical properties of alkenes also depend on the length of the carbon chain and the presence of any functional groups. For example, as the length of the carbon chain increases, the boiling point of the alkene also increases. This is due to the increased number of electrons, which leads to stronger London dispersion forces (a type of intermolecular force) between the molecules.

In summary, alkenes are colourless, odourless hydrocarbons that are less dense than water and insoluble in water. Their physical properties, including their state of matter at room temperature and their solubility, depend on the size of the molecule and the presence of any functional groups.